Question

Prader-Willi syndrome is caused by a mutation in an autosomal maternally imprinted gene. Label the following statements as true or false, assuming that the trait is 100% penetrant. Sons of affected males have a 50% chance of showing the syndrome. Daughters of affected males have a 50% chance of showing the syndrome. Page 614Sons of affected females have a 50% chance of showing the syndrome. Daughters of affected females have a 50% chance of showing the syndrome.

Answer 1

The PWS or the Prader-Willi syndrome refers to a rare genetic disorder in which the chromosome 15 gene are either unexpressed or deleted on the paternal chromosome. The paternal origin of the genetic material, which is influenced in the syndrome is essential as the specific region of chromosome 15 taking part is subject to parent of origin imprinting, signifying that for a number of genes in this region, only one copy of the gene is articulated, while the other is silenced due to imprinting.

This signifies that the majority of the individuals exhibit one functioning and one silenced set of these genes. While the individuals with the syndrome exhibits a non-functioning set and a silenced set. The disease is completely autosomal, therefore, it will not predict the sex of the offspring. Also, imprinting is on maternal copy, therefore, if the affected individual is male, it will pass on the mutated copy only in 50 percent of its gametes, and a non-functioning copy to the remaining 50 percent of the gametes. Thus, all of his offspring will exhibit PWS or will get affected.

In other case, if the affected person is female, it will pass on the mutated copy only in 50 percent of its gametes and a non-functioning copy to the remaining 50 percent of the gametes and offspring will take on the functioning copy from its male parent, therefore, all of her offspring will be normal.

Thus, the given statements will be:

1. Sons of affected males have a 50% chance of showing the syndrome - True

2. Daughters of affected males have a 50% chance of showing the syndrome. - True

3. Sons of affected females have a 50% chance of showing the syndrome. - False

4. Daughters of affected females have a 50% chance of showing the syndrome. - False